Thermodynamic Studies on Surfactants in Mixed Solvents

Critical micelle concentration (CMC) values have been determined for aqueous solution of sodium dodecyl sulphate (SDS) and dodecyl trimethyl ammonium bromide (DTAB) in mixed solvent (water + 1,3-dioxolane) at 298.15, 308.15 and 318.15 K by conductivity measurement. Thermodynamic properties of micellization, transfer of surfactant molecules from aqueous to mixed solvent, counter-ion association constant (α) and equivalent conductance at infinite dilution (λ₀) have also been evaluated from CMC data. The various parameters have been discussed to explain the micellization behaviour of surfactant in mixed solvent. Molar excess volume (V^E) of the water + 1,3-dioxolane mixture have also been determined experimentally and the same have been utilized to understand the nature of interactions operating between the components of the mixture. V^E values lend additional support to the micellization behaviour of surfactant in mixed solvent.